REPRODUCTION IN ORGANISMS Prepared by Smt RANI CHANDRAN

REPRODUCTION IN ORGANISMS Prepared by Smt RANI CHANDRAN PGT (BIOLOGY) KV AFS AKKULAM

LIFE SPAN ØPeriod from birth to natural death ØLife spans of organisms are not necessarily correlated with their sizes; For example, the size of crows and parrots are not very different yet their life spans show a wide difference ØLife span of crow is only 15 years but that of aparrot is 140 years

Differences between Asexual reproduction and sexual reproduction Asexual Reproduction Sexual reproduction Only a single parent is involved Two parents are involved May or may not involve gamete formation Involve gamete formation No fusion of gametes take place Fusion of gametes take place Daughter individuals are genetically identical and are called Clones Daughter individuals exhibit variation and are called offsprings

Types of reproduction Asexual reproduction Fragment ation Fission Budding Sexual reproduction Spore formation Veg. Prop ogation

Types of Asexual Reproduction Binary Fission in Amoeba Budding in Yeast Spore formation

Vegetative Propogation

PHASES IN SEXUALLY REPRODUCING ORGANISMS Phases in Sexually Reproducing Organisms Senescent phase Juvenile Phase Reproductive phase

EVENTS IN SEXUAL REPRODUCTION Events in Sexual Reproduction Post fertilization event Pre fertilization event Fertilization event

Pre fertilization event Gametogenesis-formation of male and female gametes. Gametes are haploid cells Types of Gametes 1. Isogametes or Homogametes. Eg. Cladophora an alga 2. Heterogametes produced are of two morphologically distinct types. The male gamete is called the antherozoid or sperm and the female gamete is called the egg or ovum. Eg Fucus an algae and Human beings Sexuality in Organisms. Bisexual-If both male and female reproductive structures are present in the same individual – Such Plants are called Monoecious Eg cucurbits Chara and coconuts -Such Animals are called Hermaphrodite Eg sponge, tapeworm and leech -Such Fungus is called Homothallic Unisexual-Either the male or female reproductive structures are present in the individual -Such Plants are called Dioecious Eg Marchantia, papaya and date palm -Such Animals are called Unisexual Eg Cockroach -Such Fungus is called Heterothallic Unisexual male flower is called staminate and Unisexual female flower is called pistillate in Dioecious plants • Cell Division during Gamete formation • Haploid parent produce haploid gametes by mitosis. These gametes fuse to form diploid zygote which then undergoes meiosis (Zygotic meiosis) to form haploid individuals Eg monera, fungi, algae and bryophytes • Diploid parent produces haploid gamete by meiosis (Gametic meiosis). These gametes fuse to form diploid zygote. Eg pteridophytes, gymnosperms, angiosperms and most of the animals including human beings

GAMETE TRANSFER Inplants like algae, bryophytes and pteridophytes, water is the medium through which this gamete transfer takes place. A large number of the male gametes, however, fail to reach the female gametes. To compensate this loss of male gametes during transport, the number of male gametes produced is several thousand times the number of female gametes produced. In seed plants pollination facilitates transfer of pollen grains to the stigma. Pollen grains germinate on the stigma and the pollen tubes carrying the male gametes reach the ovule and discharge male gametes near the egg.

Fertilization Event-Fusion of Male and Female gamete External Fertilization Internal Fertilization • In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water), i. e. , outside the body of the organism. This type of gametic fusion is called external fertilisation • In many terrestrial organisms such as fungi, bryophytes, pteridophytes, gymnosperms and angiosperms higher animals such as reptiles, birds, mammals and in a majority of plants, syngamy occurs inside • the body of the organism, hence the process is called internal fertilisation

Post fertilization event Embryogeneses Zygote Cell division Cell differentiation

Post Fertilization event 1. Formation of Zygote. In organisms with external fertilisation, zygote is formed in the external medium (usually water), whereas in those exhibiting internal fertilisation, zygote is formed inside the body of the organism. Zygote is the vital link that ensures continuity of species between organisms of one generation and the next. Every sexually reproducing organism, including human beings begin life as a single cell–the zygote.

Post Fertilization event Embryogenesis Cell division increase the number of cells in the developing embryo; Cell differentiation form specialized tissues and organs to form an organism.

TYPES OF DEVELOPMENT • Based on the development of the zygote animals are categorised into oviparous and viviparous. • Oviparous animals • lay either fertilized eggs with Calcareous shell - reptiles and birds Unfertilized eggs eg Fishes and amphibians. • The zygote develops into a young one inside the body of the female organism. • After attaining a certain stage of growth, the young ones are delivered out of the body of the female organism.

DEVELOPMENT IN PLANTS • In flowering plants, the zygote is formed inside the ovule. After fertilization the • sepals, petals and stamens of the flower wither and fall off. The zygote • develops into the embryo and the ovules develop into the seed. The ovary • develops into the fruit which develops a thick wall called pericarp that is • protective in function

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